Doped He nanodroplets in Intense few-cycle IR pulses: Dynamics of ignition and expansion

Intense NIR femtosecond pulses ionize atoms and molecules by suppressing the native Coulomb barrier seen by electrons leading to tunnel ionization. While several aspects of this ionization process in atoms, molecules and even clusters are understood, designing new atomic-scale targets provokes curiosity about the behaviour of mesoscopic systems in such intense pulses. Apart from the understanding complex atomic systems themselves under these severe conditions, the ongoing development in producing high energy density matter and single-shot x-ray imaging of such systems motivate our investigations where nanoscale plasma formation is inevitable.
We use helium nanodroplets doped with heavier rare-gas atoms to create controlled targets in a move towards the systematic understanding of nanoplasmas generated in complex atomic scale targets interacting with energetic photon pulses. In this talk we ask and answer the simple question -
How many dopant atoms does are required to saturate the charging of relatively ( ~10nm) He nanodroplets?
Our studies reveal surprisingly short timescales (< 10 fs) for the saturation in the charging of nanoscale targets in intense NIR pulses which revises the hitherto held paradigm that maximal ionization of such targets occurs only on sub-or few-picosecond timescales.